1. Field of the Invention
The invention pertains to an apparatus for converting rotary motion, such as developed by an electric motor, into linear motion for use in driving a carriage of a cut-off machine in a reciprocal manner, wherein the cut-off machine severs sections from a continuously emitted elongated workpiece.
More particularly, the apparatus is an accelerator for moving a cut-off die set used to sever a moving workpiece. The accelerator includes a rack and an endless belt drive unit to reciprocate the cut-off die set during the severing operation.
2. Description of the Related Art
Typically, a flying shear; i.e., a severing device utilizing a shearing blade which travels with the workpiece, is used to sever sections from a continuously emitting workpiece while the workpiece is being continuously discharged from a tube or fabrication mill without interrupting manufacture of the workpiece. Modem fabrication mills typically discharge a workpiece at a high rate of speed, up to 1200 feet per minute. A cut-off die set, which carries the shearing blade, must be reciprocated in such a manner that it is accelerated from an initial, stationary start position to a velocity equal that of the moving workpiece enabling the cut-off die set to travel with the workpiece during the severing stroke. Once the severing operation is completed, the cut-off die set is retracted to the initial, stationary start position in preparation for the next cut. Reciprocation of the cut-off die set during the severing operation is a function normally performed by an accelerator.
Accelerators and accelerator systems are known; see, for example, U.S. Pat. Nos. 3,460,421 and 4,542,670. As disclosed therein, both mechanical and other types of rotary to linear motion conversion-type accelerators are known. For example, accelerators using threaded shafts containing a trapped nut and those using a gear arrangement are known. Such systems perform adequately. However, increasing the output speed of a fabrication mill increases the problems associated with accelerating a cut-off die set to the velocity of the workpiece. In particular, due to the increased mass of the cut-off die set, the increased inertia makes it difficult to both hold the cut-off die set in the proper position during the cut and return the cut-off die set to its initial position in preparation for subsequent cuts. Today's cutting speeds require accelerator speeds of approximately 1200 feet per minute and the accelerator must be able to perform and withstand cutting cycles as high as 100 cuts per minute. Such increased cycle and acceleration speeds, while attainable with present equipment, make reliability and precision difficult to obtain.